Focal Nodular Hyperplasia within an Accessory Liver Lobe Presenting as a Gastric Subepithelial Tumor: A Case Report

A 33-year-old man was referred for evaluation of a 4-cm subepithelial mass located in the gastric fundus, initially suspected to be a gastrointestinal stromal tumor based on endoscopic findings. Abdominal computed tomography revealed a well-enhancing mass along the gastric wall, with no apparent anatomical continuity with the liver. Endoscopic ultrasonography demonstrated a well-circumscribed, hypoechoic lesion confined to the serosal layer, suggesting an extramural origin. Subsequent magnetic resonance imaging showed arterial phase enhancement with persistent delayed enhancement and a central hypointense area characteristic of focal nodular hyperplasia (FNH). Laparoscopic resection was performed, and intraoperative indocyanine green fluorescence confirmed the hepatic origin of the mass. Histopathological analysis confirmed FNH arising from an accessory lobe of the liver. This case underscores the importance of recognizing the atypical presentations of hepatic lesions and highlights the diagnostic value of sequential imaging modalities for distinguishing hepatic tumors from gastric subepithelial lesions.